Fix Error object value lookups.

src/messages.cc

Index: src/messages.cc
diff --git a/src/messages.cc b/src/messages.cc
index 640c2dff4e891266ce2fab0c206173dc1f7067c5..9489071403b903726aa327c34a85d4fb1f7777c7 100644
--- a/src/messages.cc
+++ b/src/messages.cc
@@ -400,10 +400,6 @@ MaybeHandle<String> ErrorToStringHelper::Stringify(Isolate* isolate,
   Handle<String> name_string = isolate->factory()->name_string();
   LookupIterator internal_error_lookup(
       error, internal_key, LookupIterator::PROTOTYPE_CHAIN_SKIP_INTERCEPTOR);
-  LookupIterator message_lookup(
-      error, message_string, LookupIterator::PROTOTYPE_CHAIN_SKIP_INTERCEPTOR);
-  LookupIterator name_lookup(error, name_string,
-                             LookupIterator::PROTOTYPE_CHAIN_SKIP_INTERCEPTOR);
 
   // Find out whether an internally created error object is on the prototype
   // chain. If the name property is found on a holder prior to the internally
@@ -412,24 +408,26 @@ MaybeHandle<String> ErrorToStringHelper::Stringify(Isolate* isolate,
   // Similar for the message property. If the message property shadows the
   // internally created error object, use that message property. Otherwise
   // use empty string as message.
-  if (internal_error_lookup.IsFound()) {
-    if (!ShadowsInternalError(isolate, &name_lookup, &internal_error_lookup)) {
-      Handle<JSObject> holder = internal_error_lookup.GetHolder<JSObject>();
-      name = Handle<String>(holder->constructor_name());
-    }
-    if (!ShadowsInternalError(isolate, &message_lookup,
-                              &internal_error_lookup)) {
-      message = isolate->factory()->empty_string();
-    }
-  }
-  if (name.is_null()) {
+  LookupIterator name_lookup(error, name_string,
+                             LookupIterator::PROTOTYPE_CHAIN_SKIP_INTERCEPTOR);
+  if (internal_error_lookup.IsFound() &&
+      !ShadowsInternalError(isolate, &name_lookup, &internal_error_lookup)) {
+    Handle<JSObject> holder = internal_error_lookup.GetHolder<JSObject>();
+    name = Handle<String>(holder->constructor_name());
+  } else {
     ASSIGN_RETURN_ON_EXCEPTION(
         isolate, name,
         GetStringifiedProperty(isolate, &name_lookup,
                                isolate->factory()->Error_string()),
         String);
   }
-  if (message.is_null()) {
+
+  LookupIterator message_lookup(
+      error, message_string, LookupIterator::PROTOTYPE_CHAIN_SKIP_INTERCEPTOR);
+  if (internal_error_lookup.IsFound() &&
+      !ShadowsInternalError(isolate, &message_lookup, &internal_error_lookup)) {
+    message = isolate->factory()->empty_string();
+  } else {
     ASSIGN_RETURN_ON_EXCEPTION(
         isolate, message,
         GetStringifiedProperty(isolate, &message_lookup,